1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the semiconductor device. Specifically, the invention relates to a semiconductor device with densely stacked semiconductor chips and a manufacturing method thereof.
2. Description of the Background Art
Most conventional methods of mounting a semiconductor chip(s) have employed die bonding of one semiconductor chip to a single lead frame. Referring to FIG. 36, a semiconductor chip 101 is attached directly onto a die pad 103 integrated with a lead frame by means of adhesive or double-faced tape. A terminal electrode (not shown) of the semiconductor chip and a lead terminal 104 are connected by a wire 105 and they are further encapsulated by an encapsulating resin for the purpose of protection from moisture, impact and the like. Although this type of semiconductor device can be manufactured in a simple manner and its many advantages have been proved, it has a problem of a low ratio of the semiconductor chip relative to a unit volume in which the semiconductor chip is housed.
Accordingly, as shown in FIG. 37, a semiconductor device has been proposed including two stacked semiconductor chips 101a and 101b (Japanese Patent Laying-Open No. 2000-156464). This semiconductor device includes a lower semiconductor chip 101b attached to one frame 104a by adhesive 107 and an upper semiconductor chip 101a attached to the other frame 104b. The semiconductor chips are further bonded to each other by adhesive 107. Respective terminal electrodes (not shown) of the semiconductor chips and lead terminals (not shown) are connected by means of wires (not shown) and encapsulated by an encapsulating resin 106. In plan view, the semiconductor chips of the semiconductor device shown in FIG. 37 mostly overlap one another with a small displacement therebetween. In this way, the semiconductor device shown in FIG. 37 achieves a dramatic densification as compared with the semiconductor device shown in FIG. 36.
Through never-ending progress in downsizing of semiconductor chips, a semiconductor chip is now almost thinner than a lead frame. Such semiconductor chips have become highly dense, while densification of a semiconductor device mounting these semiconductor chips is insufficient. In particular, current semiconductor devices are not thin enough as thinning thereof has rarely received attention. Then, with a rapid prevalence of mobile data terminals like mobile phones, digital cameras, video camera and the like, there arise strong demands for downsizing and densification in consideration of the thickness of a semiconductor device. Downsizing and densification of a semiconductor device with its thickness reduced without an increase in area would provide desirable effects not only in such uses as mentioned above but in many other uses.
The present invention aims to provide a semiconductor device and a manufacturing method thereof achieving downsizing and densification by reducing the thickness of the semiconductor device without increase in area.
According to a first aspect of the present invention, a semiconductor device has terminal electrodes arranged, in plan view, outside a region where semiconductor chips are arranged. The semiconductor device includes a lower semiconductor chip located to overlap in the range of height with the terminal electrodes, an upper semiconductor chip located above the lower semiconductor chip, a wire connecting the upper and lower semiconductor chips to the terminal electrodes, and an encapsulating resin encapsulating the upper and lower semiconductor chips and the wire. The encapsulating resin and the terminal electrodes have respective bottom surfaces coplanar with each other.
The semiconductor chips and the terminal electrodes are arranged so that the terminal electrodes do not increase the thickness of the semiconductor device by their full thickness dimension. Namely, the thickness of terminal electrodes does not affect the thickness of the semiconductor device or merely a part thereof adds the thickness of the semiconductor device. It is thus possible to make the semiconductor device thinner regardless of the thickness of a lead frame where the terminal electrodes are formed. Consequently, downsizing and densification of products such as mobile data terminal can be promoted. Further, as the bottom surfaces of the encapsulating resin and terminal electrodes are coplanar, the terminal electrodes can be affixed onto an adhesive tape to form the semiconductor device having the above-described structure and use the adhesive tape as an outer surface of the encapsulating resin serving also as a resin-leak-prevention sheet thereby accomplishing resin encapsulation, for example. In this way, manufacture can be simplified.
Regarding the semiconductor device according to the first aspect of the invention, the upper semiconductor chip may be supported by a die pad portion coplanar with the terminal electrodes and the lower semiconductor chip may be arranged without overlapping in plan view with the die pad portion, for example.
This structure enables the upper semiconductor chip to firmly be supported. The upper semiconductor chip together with the die pad portion may be bonded to the lower semiconductor chip. Alternatively, the upper and lower semiconductor chips may be separated to fill the space between the chips with the encapsulating resin. Here, xe2x80x9csupportxe2x80x9d means that the chip is supported by the die pad portion by adhering them together using adhesive, die bonding material or the like.
Regarding the semiconductor device according to the first aspect of the invention, the lower semiconductor chip and the encapsulating resin may have respective bottom surfaces coplanar with each other and the bottom surface of the lower semiconductor chip may be exposed from the encapsulating resin, for example.
With this structure, it is possible, for example, to affix the lower semiconductor chip together with the terminal electrodes onto an adhesive tape so as to fabricate the semiconductor device, so that manufacture is simplified. Further, the lower semiconductor chip only may be used to support the upper semiconductor chip to eliminate the die pad portion, reducing a manufacturing cost.
Regarding the semiconductor device according to the first aspect of the invention, the upper semiconductor chip may be supported by a die pad portion located higher than the terminal electrodes, and the lower semiconductor chip may have its bottom surface encapsulated by the encapsulating resin, for example.
With this structure, the lower semiconductor chip is supported such that it suspends from the upper semiconductor chip supported by the die pad portion, and accordingly the lower semiconductor chip can be arranged inwardly spaced from the bottom surface of terminal electrodes. The lower semiconductor chip is thus encapsulated by the encapsulating resin to enable the entire semiconductor device to be protected from moisture, direct impact and the like.
The semiconductor device according to the first aspect of the invention is of QFN (Quad Flat Non-Lead Package) type having the terminal electrodes arranged outside to surround the semiconductor chips, for example.
The terminal electrodes arranged to surround the semiconductor chips and the semiconductor chips and the electrodes are nearly located. Consequently, wiring of the electrodes and chips becomes simplified. Then, there is a higher degree of freedom for partially overlapping two semiconductor chips.
Regarding the semiconductor device according to the first aspect of the invention, the upper and lower semiconductor chips may be rectangles respectively in shape, connection terminals of the semiconductor chips may be arranged along shorter sides opposing each other of the rectangles, and the upper and lower semiconductor chips being rectangles in shape may be arranged to cross each other in plan view, for example.
Connection terminals are thus distributed over four sides so that wires on the semiconductor chips are not closely located in space and never interfere with each other. In particular, for the QFN type semiconductor device with terminal electrodes surrounding the chips, the connection terminals arranged on four sides and the surrounding terminal electrodes can neatly be connected with short wires.
Regarding the semiconductor device according to the first aspect of the invention, the terminal electrodes arranged outside may be leads arranged along two opposing sides with the semiconductor chips therebetween, for example.
This structure can be used to manufacture a thin TSOP type semiconductor device in a simple manner easily, with manufacturing cost reduced by enhancement of efficiency and yield.
According to a second aspect of the invention, a semiconductor device is of TSOP (Thin Small Outline Package) type having semiconductor chips arranged between a first lead portion and a second lead portion provided respectively on two sides opposing in plan view. The semiconductor device includes a first die pad portion integrated with and noncoplanar with the first lead portion and located higher relative to a reference plane passing through central position between the highest surface and the lowest surface of the first and second lead portions, a second die pad portion integrated with and noncoplanar with the second lead portion and located lower relative to the reference plane, and a lower semiconductor chip supported by the first die pad portion and an upper semiconductor chip supported by the second die pad portion. The two semiconductor chips are partially overlapped and located to overlap in the range of height with the first and second lead portions.
The semiconductor chips and the terminal electrodes are arranged so that the terminal electrodes do not increase the thickness of the semiconductor device by their full thickness dimension. Namely, the thickness of the lead frame does not affect the thickness of the semiconductor device or merely a part thereof adds the thickness of the semiconductor device. It is thus possible to make the semiconductor thinner. Further, components are arranged symmetrically in the vertical direction with respect to the reference plane and accordingly thermal stress and residual stress are not likely to be uneven in the vertical direction. Then, distortion like warp and the like rarely occurs. The upper and lower semiconductor chips may be bonded or may be spaced with an encapsulating resin filling the gap therebetween. It is noted that xe2x80x9csupportxe2x80x9d means that the die pad portion is directly bonded to one of the bonded semiconductor chips to support the chip, and means, from an all-round and dynamical point of view, that the two die pad portions cooperate to eventually support both semiconductor chips. The reference plane is in parallel with planes that constitute the lead portions.
Regarding the semiconductor device according to the second aspect of the invention, the first die pad portion may be provided to a first lead frame located including the first lead portion above the reference plane, and the second die pad portion may be provided to a second lead frame located including the second lead portion below the reference plane, for example.
With this structure, two stacked lead frames can be employed to manufacture a semiconductor device. Two semiconductor chips can thus be stacked readily and efficiently on the two lead frames.
Regarding the semiconductor device according to the second aspect of the invention, for example, the first die pad portion may be L-shaped including a first extension extending from an end of the first lead portion toward the second lead portion and a first opposing portion continuing from the first extension and extending in parallel with the first lead portion. The second die pad portion may be arranged in plan view opposite the first die pad portion and L-shaped including a second extension extending from an end of the second lead portion toward the first lead portion and a second opposing portion continuing from the second extension and extending in parallel with the second lead portion. The first extension and the first opposing portion may have their bottom surface supporting the lower semiconductor chip and the second extension and the second opposing portion may have their upper surface supporting the upper semiconductor chip.
Such L-shaped die pad portions can be used to manufacture a thin and dense semiconductor device efficiently.
Regarding the semiconductor device according to the second aspect of the invention, the first and second lead portions and the first and second die pad portions may be integrated into a common lead frame, the reference plane passing through center of thickness of the lead frame, the first die pad portion may support the lower semiconductor chip of the partially overlapped semiconductor chips, and the second die pad portion may support the upper semiconductor chip, for example.
This simple and plain structure can be produced with high yield and efficiency as well as an earlier delivery. In addition, as components are arranged symmetrically in the vertical direction with respect to the reference plane, warp caused by thermal strain, residual stress and the like is unlikely to occur.
Regarding the semiconductor device according to the second aspect of the invention, center of thickness of the first die pad portion and center of thickness of the second die pad portion are preferably spaced vertically from the reference plane in respective directions opposite to each other, each by a distance equal to the sum of a half of thickness of the lead frame and a half of thickness of an adhesive layer bonding the upper and lower semiconductor chips, for example.
A precise symmetry relative to the reference plane is thus maintained to achieve a great resistance to warp and the like described above.
According to the first aspect of the invention, a method of manufacturing a semiconductor device having terminal electrodes arranged, in plan view, outside a region where semiconductor chips are arranged, includes, an affix-onto-sheet step of affixing the terminal electrodes and a lower semiconductor chip onto an adhesive sheet, a semiconductor chip stacking step of bonding an upper semiconductor chip onto the lower semiconductor chip, a wire connecting step of connecting the lower and upper semiconductor chips respectively to the terminal electrodes by wires, a resin encapsulating step of encapsulating the terminal electrodes, lower semiconductor chip, upper semiconductor chip and wires arranged on the adhesive sheet by resin, and an adhesive sheet stripping step of stripping the adhesive sheet from components resin-encapsulated in the resin encapsulating step.
With this structure, the adhesive sheet on which the terminal electrodes and semiconductor chips are arranged can be used as a sheet for preventing resin leakage and forming the outer surface of encapsulating resin. Then, the thickness of terminal electrodes does not add the thickness of the semiconductor device or just partially adds the thickness of the semiconductor chip. A resultant thin semiconductor device can accordingly be manufactured simply and with a low cost.
Regarding the method of manufacturing a semiconductor device according to the first aspect of the invention, a die pad portion may be affixed onto the sheet together with the terminal electrodes and lower semiconductor chip in the affix-onto-sheet step to bond the upper semiconductor chip to the die pad portion in the semiconductor chip stacking step, for example.
The upper semiconductor chip in this structure is supported by the die pad portion so that the lower semiconductor chip can be positioned with a greater degree of freedom. Specifically, the lower semiconductor chip supported by an adhesive tape in course of manufacture may be exposed on the bottom surface after the manufacture. Alternatively, the lower semiconductor chip may be supported by being suspended from the upper semiconductor chip. Consequently, the lower semiconductor chip is spaced inward from the bottom surface and the outer surface is formed by the encapsulating resin and thus the structure resistant to moisture and impact can be achieved.
Regarding the method of manufacturing a semiconductor device according to the first aspect of the invention, only the terminal electrodes and a die pad portion may be affixed onto the adhesive sheet in the affix-onto-sheet step to bond the upper semiconductor chip to the die pad portion in the semiconductor chip stacking step, the upper semiconductor chip and lower semiconductor chip being bonded in advance to constitute stacked semiconductor chips, for example.
This manufacturing method may be used to position the lower semiconductor chip spaced inward from the bottom surface.
Regarding the method of manufacturing a semiconductor device according to the first aspect of the invention, only the lower semiconductor chip may be affixed onto the adhesive sheet in the affix-onto-sheet step to affix a die pad portion to which the upper semiconductor chip is bonded in advance onto the adhesive sheet together with the terminal electrodes, for example.
According to conditions of manufacture sites, thin semiconductor devices can efficiently be produced by using this manufacturing method. The upper and lower semiconductor chips may be bonded with adhesive or spaced with the gap therebetween filled with the encapsulating resin.
A method of manufacturing a semiconductor device according to the second aspect of the invention includes: a lead frame stacking step of stacking a first lead frame on a second lead frame, the first lead frame including a first lead portion and a first die pad portion extending in L-shape from an end of the first lead portion along periphery of a region where a lower semiconductor chip is arranged, the second lead frame including a second lead portion and a second die pad portion opposing the first die pad portion in plan view and extending in L-shape from an end of the second lead portion along periphery of a region where an upper semiconductor chip is arranged, the first and second lead portions opposing in plan view with the upper and lower semiconductor chips therebetween; a semiconductor chip bonding step of bonding the lower semiconductor chip to the first die pad portion and bonding the upper semiconductor chip to the second die pad portion; a welding step of welding together the first lead frame and the second lead frame at their overlapping portion; a wire bonding step of connecting the upper and lower semiconductor chips to a terminal electrode by a wire; a resin encapsulating step of encapsulating by means of a resin a region inside the overlapping portion being welded; and a cutting off step of cutting off a portion outside the resin encapsulated first and second lead portion and the upper and lower semiconductor chips in the resin encapsulating step.
This manufacturing method enables a thin and dense semiconductor device to be produced efficiently by using two lead frames and welding.
Regarding the method of manufacturing a semiconductor device according to the second aspect of the invention, sub steps of the lead frame stacking step and sub steps of the semiconductor chip bonding step are preferably combined and partially changed in their order to be performed, for example.
Depending on manufacture sites, it could be efficient to preliminarily bond a semiconductor chip to one die pad portion in the lead frame stacking step. Such a change in order of sub steps is preferably made over the main steps, not just in one main step as described above.
Regarding the method of manufacturing a semiconductor device according to the second aspect of the invention, the lead frame stacking step and the semiconductor chip bonding step may include as a whole a die bonding material arranging step of arranging a die bonding material bonding the upper and lower semiconductor chips to the first and second die pad portions, for example.
The die bonding material is desirably employed instead of adhesive with a high flowability since it inevitably occurs that one of the lead frames is caused to face downward or both lead frames are tilted. A manufacturing process can thus be constituted to provide a high stability.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.